1. Field of the Invention
The present invention relates to a wide field of view optical magnifying system and, more particularly, to a magnifier having a very long eye relief and large working distance.
2. Description of Related Art
Visual inspection tools are used in several industrial fields to inspect components for defects which cannot be seen with the naked eye. Many industries have stringent magnification specifications. In the soldering industry and especially in the aerospace circuit board industry, the solder connections must be inspected to meet desired specifications. Visual tools, such as magnifiers are used to increase the apparent size of the solder connection viewed. This increase in size better enables an inspector to see and determine whether or not the solder connection meets desired specifications. Other applications will become apparent which utilize magnifying devices for inspection where inspection with the naked eye is inadequate.
Prior magnifying optical systems exist in the field. These prior magnifiers generally have one or more lens elements and have several disadvantages. The prior magnifiers generally have a magnification power of less than what is specified on the magnifier. The magnifiers generally have a small usable field of view, which causes severe eye strain in just a short period of time. The viewing distance between the user's eye and the object is generally very short. This close viewing range causes the user to hold the viewed object in close proximity to his face increasing the likelihood of contamination. Generally, the prior magnifiers have distorted imagery as the view traverses from the center to the peripheries of the field of view. The prior magnifiers are somewhat heavy, have poor resolution, and have chromatic aberrations. Also, prior magnifiers generally limit the eye resolution to only along the axis of the magnifier. Thus, there is a need in the art to provide an optical magnifying system, having a wide field of view and which the operator can easily control during use.
Two solutions to the above problem are assignee's U.S. Pat. Nos. 4,768,866, entitled Optical Magnifying System: 4.times.Loupe issued Sept. 6, 1988 and 4,792,214, entitled Optical Magnifying System: 10.times.Loupe, issued Dec. 20, 1988, both of which specifications are herein incorporated by reference.
U.S. Pat. No. 4,768,866 illustrates an optical magnifying system including a primary lens defining an optical axis and positioned a larger than normal predetermined working distance adjacent to the object being viewed. A secondary lens, a tertiary and a quaternary lens are also centered with respect to the optical axis. The primary, secondary, tertiary and quaternary lenses have surfaces which are shaped to focus upon an object such that a high resolution image is formed at infinity at 4.times.magnification.
U.S. Pat. No. 4,792,214 illustrates an optical magnifying system which has high resolution over a large field of view. The invention includes lenses shaped to focus upon an object such that a high resolution image is formed at infinity at 10.times.magnification. Also, the invention provides the art with a six element eye loupe which limits distortion in the field of view, corrects chromatic aberrations, and provides true 10.times.magnification.
While the inventions of the above two references perform satisfactorily, the present invention provides still further improvements to the art.